JP2507754B2 - Flux for brazing aluminum parts - Google Patents

Description

TECHNICAL FIELD The present invention relates to a flux used for brazing an aluminum member made of aluminum or an aluminum alloy, and particularly to improving the corrosion resistance of an aluminum product after brazing. .

[Conventional technology]

Generally, a heat exchanger such as an aluminum device, for example, an automobile radiator, an oil cooler, a condenser for an air conditioner, or an evaporator is assembled by a brazing method. Each of these heat exchangers is a passage through which water for cooling the engine, which is a medium for heat exchange, engine oil, freon (gas or liquid), so-called a tube, and an air side of the tube for performing heat exchange. For example, an air conditioner condenser is provided with fins provided between the tubes (1) bent in a meandering shape through which a medium passes, as shown in FIG.
A fin (2) processed into a corrugated shape is attached, and a brazing method is used for joining the tube and the fin.

Such a brazing method is usually performed by previously clad an Al-Si alloy brazing material on the surface of an aluminum member forming a tube or fin, or by Al-Si between the tube and the fin.
A thin plate of a system alloy brazing material is inserted and heated to a temperature slightly higher than the melting temperature of the brazing material, that is, 590 to 620 ° C., and the surface oxide film of the aluminum member is destroyed during this heating. Flux is used to improve fluidity and wettability.

Conventionally, NaC is used as a flux for brazing aluminum parts
A mixture of chlorides such as l, KCl, LiCl and ZnCl ₂ and fluorides such as AlF ₃ , KF, NaF and LiF in an appropriate composition is used.
However, any residual flux of these fluxes must be removed by hot water or acid after brazing, and when the flux remains, chlorides are hygroscopic and thus become an electrolyte and corrode the aluminum member. In addition, removal by hot water or acid always involves drainage treatment due to pollution problems, which is a cause of high cost. Also, in order to braze one heat exchanger, 100 to 400 g of flux must be used, which causes higher cost.

Recently, in order to improve these, a flux composed only of fluoride, for example, a flux composed of AlF ₃ 53 to 55 wt% and the balance KF was proposed by British Patent No. 1055914, and
A flux consisting of F ₄ 65.6 to 99.9 wt% and the balance K ₃ AlF ₆ is proposed in Japanese Patent Publication No. 58-27037, and a flux consisting of 95 wt% or more of K ₂ AlF ₅ · H ₂ O is disclosed in JP-A-60-. 170597
Japanese Patent Application Laid-Open No. 60-170596 proposes a flux containing K ₂ AlF ₅ or K ₂ AlF ₅ .H ₂ O in an amount of ₅ to 95 wt% and the balance KAlF ₄ . Since the flux of these potassium fluoroaluminate complexes has high activity, a smaller amount than the above chloride-based flux has the effect of destroying the oxide film, and even a smaller amount can be achieved by brazing in a non-oxidizing atmosphere, and heat exchange can be performed. The amount of flux used is 10 to 30g per unit. Further, even if the flux residue after brazing is left as it is, it does not absorb moisture and does not cause corrosion, so that there is an advantage that the flux removing process can be omitted.

[Problems to be solved by the invention]

Conventional chloride flux contains ZnCl ₂ , and when brazing is performed using this, Zn diffuses on the surface of the member, and the maximum Zn concentration is 1 to 3% and the Zn diffusion depth is 100 to 200 μm. A Zn diffusion layer is obtained. This Zn diffusion layer acts as a sacrificial anode because it has a lower potential than the non-diffusion layer, prevents through pitting corrosion of the heat exchanger, and prolongs its life significantly.

However, the potassium fluoroaluminate complex does not contain Zn, and therefore a sacrificial layer cannot be obtained.Therefore, for example, in the production of a capacitor, Zn is applied to the surface of a multi-hole tube by zincate treatment or thermal spraying before brazing. Although a method of adhering to obtain a Zn diffusion layer has been adopted, there is a problem that the manufacturing process becomes long and the cost becomes high.

[Means for solving problems]

As a result of various studies in view of this, the present invention improves the flux of the conventionally used potassium fluoroaluminate complex and develops a brazing flux for aluminum members that can improve the corrosion resistance of aluminum products after brazing. It is characterized in that it contains 1 to 20 wt% of tin fluoride, and the balance is potassium fluoroaluminate complex.

[Work]

In the present invention, the content of tin fluoride in the potassium fluoroaluminate complex is contained in an amount of 1 to 20 wt% for the purpose of melting tin fluoride during brazing and heating and precipitating and diffusing Sn on the surface of the aluminum member. This Sn diffusion layer is base to the potential of the non-diffusion layer and prevents pitting corrosion. However, the reason why the content of the fluoride is limited to 1 to 20 wt% is that if the content is less than 1 wt%, the effect is small, and if it exceeds 20 wt%, the brazing property deteriorates. The potassium fluoroaluminate complex is a flux consisting of K ₂ AlF ₅ · H ₂ O having a purity of 95 wt% or more, a flux consisting of _{5 to} 95 wt% of K ₂ AlF ₅ · H ₂ O, and the balance consisting of KAlF ₄ and AlF ₃ 53. All the potassium fluoroaluminate complexes such as a flux consisting of ~ 55 wt% and the balance KF, a flux consisting of KAlF ₄ 65.6 to 99.9 wt% and the balance K ₃ AlF ₆ are used.

〔Example〕

 The present invention will be described below with reference to examples.

Example (1) Using a simulated core obtained by combining an extruded multi-hole tube (1) made of JIS 1050 alloy with a wall thickness of 1 mm shown in FIG. 2 and a corrugated fin (2) of JIS BA 12PC, after pretreatment ,
A flux having the composition shown in Table 1 was applied as a 10 wt% suspension, dried, and brazed by heating at a temperature of 610 ° C. for 30 minutes in an N ₂ gas atmosphere. The core was evaluated for corrosion resistance and brazing property, and the results are shown in Table 2.

To evaluate corrosion resistance, measure the potential on the tube surface (vs. SC
E, 5% NaCl, 25 ° C.) and the CASS test for 100 hours to measure the pitting depth. The brazability was evaluated by measuring the length (l) of the fillet (3) at the joint between the multi-hole tube (1) and the fin (2) for the core, as shown in FIG. 1 to 1.5 mm
Those having a diameter of less than 1 mm are indicated by a circle, and those having a diameter of less than 1 mm are indicated by an arrow.

As is clear from Tables 1 and 2, the fluxes No. 1 to No. 5 of the present invention have good brazing properties and a surface potential of −.
From 0.9 to -1.1V and the potential (-0.74V) of the 1050 alloy, it was 50 mV or more base and the maximum pit depth was 0.2 mm or less, which was good overall.

On the other hand, with conventional flux Nos. 8 to 9, the potential is -0.74.
It was V and the maximum pitting depth was as deep as 0.6 mm. In addition, Comparative Flux No. 6 has a small amount of tin fluoride added, so the potential is
It is not less base than 50 mV, pitting corrosion is as deep as 0.6 mm, and in No. 7, the brazing property is inferior because the amount of tin fluoride added is large.

Example 2 As shown in FIG. 1, corrugated fins (2) made of JIS 1050 alloy extruded multi-hole tube (1) and JIS BA 12PC.
After degreasing, the combined capacitor was applied in the same manner as in Example (1) using flux No. 5 of the present invention and conventional flux No. 8 shown in Table 1. After drying at 200 ℃, N ₂
Brazing was performed by heating to 610 ° C. for 3 minutes in a gas atmosphere.

Argon gas was sealed in this condenser at a pressure of 20 kg / cm ² and a CASS test was performed. As a result, conventional flux
The product brazed with No. 8 had gas leaked from the multi-hole tube due to corrosion in 300 hours. On the other hand, in the case of brazing using the flux No. 5 of the present invention, no gas leaked even after 1500 hours.

〔The invention's effect〕

As described above, according to the flux of the present invention, not only the life of the heat exchanger can be remarkably lengthened, but also the manufacturing process can be shortened, resulting in a remarkable industrial effect.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a condenser, FIG. 2 is an explanatory view showing a simulated core, and FIG. 3 is a sectional view showing a joint portion between a tube and a fin. 1 ... Extruded multi-hole tube 2 ... Corrugated fin 3 ... Fillet

Claims (1)

(57) [Claims] 1. A brazing flux for an aluminum member, which contains 1 to 20 wt% of tin fluoride and the balance is a potassium fluoroaluminate complex.